Simulate package visibility of functions of different modules contained in a single directory.

build.sh

#!/bin/bash

# BUILD library which contains all modules of the package
echo "Build package.o from module1.c and module2.c"
gcc -c -o module1.o module1.c
gcc -c -o module2.o module2.c
ld -o package.o -r module1.o module2.o
symbols=(`nm package.o`)
for((i=0;i<${#symbols[*]};i=i+1)) do
   if [ "${symbols[$i]}" != "T" ]; then continue; fi
   function_name=${symbols[$((i+1))]}
   if [ "${function_name#private}" = "$function_name" ]; then continue; fi
   echo "Change function '$function_name' to package scope (private)"
   objcopy -L "$function_name" package.o
done

echo "Generate main.c and link it with package.o"
echo "main() calls public_function from module1.c in package.o"
echo "#include <stdio.h>" > main.c
echo "#include \"module1.h\"" >> main.c
echo >> main.c
echo "int main(int argc, const char* argv[])" >> main.c
echo "{" >> main.c
echo "   public_function();" >> main.c
echo "   return 0;" >> main.c
echo "}" >> main.c

gcc -o main main.c package.o
echo "::Start main::"
./main
echo "::End main::"

echo
echo "Generate main.c and link it with package.o"
echo "main() now tries to call private_function from module2.c in package.o"
echo "This will generate a compiler error !"
gcc -o main "-Dpublic_function=private_function" main.c package.o

module1.c

#include <stdio.h>
#include "module1.h" // header of this module
#include "module2.h" // contains private_function

void public_function()
{
   printf("enter public_function()\n");
   private_function();
   printf("exit public_function()\n");
}

module1.h

#ifndef PACKAGE_MODULE1_HEADER
#define PACKAGE_MODULE1_HEADER

void public_function(void);

#endif

module2.c

#include <stdio.h>
#include "module2.h" // header of this module

void private_function()
{
   printf("enter private_function()\n");
   printf("exit private_function()\n");
}

module2.h

#ifndef PACKAGE_MODULE2_HEADER
#define PACKAGE_MODULE2_HEADER

void private_function(void);

#endif